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RFC 8131

Informational
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RSVP-TE Signaling Procedure for End-to-End GMPLS Restoration and Resource Sharing

 


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Internet Engineering Task Force (IETF)                          X. Zhang
Request for Comments: 8131                                 H. Zheng, Ed.
Category: Informational                              Huawei Technologies
ISSN: 2070-1721                                           R. Gandhi, Ed.
                                                                  Z. Ali
                                                     Cisco Systems, Inc.
                                                           P. Brzozowski
                                                            ADVA Optical
                                                              March 2017

                      RSVP-TE Signaling Procedure for
             End-to-End GMPLS Restoration and Resource Sharing

Abstract

   In non-packet transport networks, there are requirements where the
   Generalized Multiprotocol Label Switching (GMPLS) end-to-end recovery
   scheme needs to employ a restoration Label Switched Path (LSP) while
   keeping resources for the working and/or protecting LSPs reserved in
   the network after the failure occurs.

   This document reviews how the LSP association is to be provided using
   Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
   signaling in the context of a GMPLS end-to-end recovery scheme when
   using restoration LSP where failed LSP is not torn down.  In
   addition, this document discusses resource sharing-based setup and
   teardown of LSPs as well as LSP reversion procedures.  No new
   signaling extensions are defined by this document, and it is strictly
   informative in nature.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8131.

[Page 2] 
Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................4
      2.1. Terminology ................................................4
      2.2. Abbreviations ..............................................4
   3. Overview ........................................................4
      3.1. Examples of Restoration Schemes ............................5
           3.1.1. 1+R Restoration .....................................5
           3.1.2. 1+1+R Restoration ...................................6
                  3.1.2.1. 1+1+R Restoration - Variants ...............7
      3.2. Resource Sharing by Restoration LSP ........................7
   4. RSVP-TE Signaling Procedure .....................................8
      4.1. Restoration LSP Association ................................8
      4.2. Resource Sharing-Based Restoration LSP Setup ...............8
      4.3. LSP Reversion .............................................10
           4.3.1. Make-While-Break Reversion .........................10
           4.3.2. Make-Before-Break Reversion ........................11
   5. Security Considerations ........................................12
   6. IANA Considerations ............................................13
   7. References .....................................................13
      7.1. Normative References ......................................13
      7.2. Informative References ....................................13
   Acknowledgements  .................................................14
   Contributors ......................................................14
   Authors' Addresses ................................................15

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1.  Introduction

   Generalized Multiprotocol Label Switching (GMPLS) [RFC3945] defines a
   set of protocols, including Open Shortest Path First - Traffic
   Engineering (OSPF-TE) [RFC4203] and Resource Reservation Protocol -
   Traffic Engineering (RSVP-TE) [RFC3473].  These protocols can be used
   to set up Label Switched Paths (LSPs) in non-packet transport
   networks.  The GMPLS protocol extends MPLS to support interfaces
   capable of Time Division Multiplexing (TDM), Lambda Switching and
   Fiber Switching.  These switching technologies provide several
   protection schemes [RFC4426] [RFC4427] (e.g., 1+1, 1:N, and M:N).

   RSVP-TE signaling has been extended to support various GMPLS recovery
   schemes, such as end-to-end recovery [RFC4872] and segment recovery
   [RFC4873].  As described in [RFC6689], an ASSOCIATION object with
   Association Type "Recovery" [RFC4872] can be signaled in the RSVP
   Path message to identify the LSPs for restoration.  Also, an
   ASSOCIATION object with Association Type "Resource Sharing" [RFC4873]
   can be signaled in the RSVP Path message to identify the LSPs for
   resource sharing.  Section 2.2 of [RFC6689] reviews the procedure for
   providing LSP associations for GMPLS end-to-end recovery, and Section
   2.4 of that document reviews the procedure for providing LSP
   associations for sharing resources.

   Generally, GMPLS end-to-end recovery schemes have the restoration LSP
   set up after the failure has been detected and notified on the
   working LSP.  For a recovery scheme with revertive behavior, a
   restoration LSP is set up while the working LSP and/or protecting LSP
   are not torn down in the control plane due to a failure.  In non-
   packet transport networks, because working LSPs are typically set up
   over preferred paths, service providers would like to keep resources
   associated with the working LSPs reserved.  This is to make sure that
   the service can be reverted to the preferred path (working LSP) when
   the failure is repaired to provide deterministic behavior and a
   guaranteed Service Level Agreement (SLA).

   In this document, we review procedures for GMPLS LSP associations,
   resource-sharing-based LSP setup, teardown, and LSP reversion for
   non-packet transport networks, including the following:

   o  The procedure for providing LSP associations for the GMPLS end-to-
      end recovery using restoration LSP where working and protecting
      LSPs are not torn down and resources are kept reserved in the
      network after the failure.

   o  The procedure for resource sharing using the Shared Explicit (SE)
      flag in conjunction with an ASSOCIATION object.  In [RFC3209], the
      Make-Before-Break (MBB) method assumes the old and new LSPs share

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      the SESSION object and signal SE flag in the SESSION_ATTRIBUTE
      object for sharing resources.  According to [RFC6689], an
      ASSOCIATION object with Association Type "Resource Sharing" in the
      Path message enables the sharing of resources across LSPs with
      different SESSION objects.

   o  The procedures for LSP reversion and resource sharing, when using
      end-to-end recovery scheme with revertive behavior.

   This document is strictly informative in nature and does not define
   any RSVP-TE signaling extensions.

2.  Conventions Used in This Document

2.1.  Terminology

   The reader is assumed to be familiar with the terminology in
   [RFC3209], [RFC3473], [RFC4872], and [RFC4873].  The terminology for
   GMPLS recovery is defined in [RFC4427].

2.2.  Abbreviations

   GMPLS: Generalized Multiprotocol Label Switching

   LSP: Label Switched Path

   MBB: Make-Before-Break

   MPLS: Multiprotocol Label Switching

   RSVP: Resource Reservation Protocol

   SE: Shared Explicit (flag)

   TDM: Time Division Multiplexing

   TE: Traffic Engineering

3.  Overview

   The GMPLS end-to-end recovery scheme, as defined in [RFC4872] and
   discussed in this document, switches normal traffic to an alternate
   LSP that is not even partially established only after the working LSP
   failure occurs.  The new alternate route is selected at the LSP head-
   end node, it may reuse resources of the failed LSP at intermediate
   nodes and may include additional intermediate nodes and/or links.

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3.1.  Examples of Restoration Schemes

   Two forms of end-to-end recovery schemes, 1+R restoration and 1+1+R
   restoration, are described in the following sections.  Other forms of
   end-to-end recovery schemes also exist, and they can use these
   signaling techniques.

3.1.1.  1+R Restoration

   One example of the recovery scheme considered in this document is 1+R
   recovery.  The 1+R recovery scheme is exemplified in Figure 1.  In
   this example, a working LSP on path A-B-C-Z is pre-established.
   Typically, after a failure detection and notification on the working
   LSP, a second LSP on path A-H-I-J-Z is established as a restoration
   LSP.  Unlike a protecting LSP, which is set up before the failure, a
   restoration LSP is set up when needed, after the failure.

          +-----+    +-----+     +-----+     +-----+
          |  A  +----+  B  +-----+  C  +-----+  Z  |
          +--+--+    +-----+     +-----+     +--+--+
              \                                /
               \                              /
             +--+--+       +-----+        +--+--+
             |  H  +-------+  I  +--------+  J  |
             +-----+       +-----+        +-----+

          Figure 1: An Example of 1+R Recovery Scheme

   During failure switchover with 1+R recovery scheme, in general,
   working LSP resources are not released so that working and
   restoration LSPs coexist in the network.  Nonetheless, working and
   restoration LSPs can share network resources.  Typically, when the
   failure has recovered on the working LSP, the restoration LSP is no
   longer required and is torn down while the traffic is reverted to the
   original working LSP.

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3.1.2.  1+1+R Restoration

   Another example of the recovery scheme considered in this document is
   1+1+R.  In 1+1+R, a restoration LSP is set up for the working LSP
   and/or the protecting LSP after the failure has been detected; this
   recovery scheme is exemplified in Figure 2.

             +-----+       +-----+        +-----+
             |  D  +-------+  E  +--------+  F  |
             +--+--+       +-----+        +--+--+
               /                              \
              /                                \
          +--+--+    +-----+     +-----+     +--+--+
          |  A  +----+  B  +-----+  C  +-----+  Z  |
          +--+--+    +-----+     +-----+     +--+--+
              \                                /
               \                              /
             +--+--+       +-----+        +--+--+
             |  H  +-------+  I  +--------+  J  |
             +-----+       +-----+        +-----+

          Figure 2: An Example of 1+1+R Recovery Scheme

   In this example, a working LSP on path A-B-C-Z and a protecting LSP
   on path A-D-E-F-Z are pre-established.  After a failure detection and
   notification on the working LSP or protecting LSP, a third LSP on
   path A-H-I-J-Z is established as a restoration LSP.  The restoration
   LSP, in this case, provides protection against failure of both the
   working and protecting LSPs.  During failure switchover with the
   1+1+R recovery scheme, in general, failed LSP resources are not
   released so that working, protecting, and restoration LSPs coexist in
   the network.  The restoration LSP can share network resources with
   the working LSP, and it can share network resources with the
   protecting LSP.  Typically, the restoration LSP is torn down when the
   traffic is reverted to the original LSP and is no longer needed.

   There are two possible models when using a restoration LSP with 1+1+R
   recovery scheme:

   o  A restoration LSP is set up after either a working or a protecting
      LSP fails.  Only one restoration LSP is present at a time.

   o  A restoration LSP is set up after both the working and protecting
      LSPs fail.  Only one restoration LSP is present at a time.

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3.1.2.1.  1+1+R Restoration - Variants

   Two other possible variants exist when using a restoration LSP with
   1+1+R recovery scheme:

   o  A restoration LSP is set up after either a working or protecting
      LSP fails.  Two different restoration LSPs may be present, one for
      the working LSP and one for the protecting LSP.

   o  Two different restoration LSPs are set up after both working and
      protecting LSPs fail, one for the working LSP and one for the
      protecting LSP.

   In all these models, if a restoration LSP also fails, it is torn down
   and a new restoration LSP is set up.

3.2.  Resource Sharing by Restoration LSP

                              +-----+      +-----+
                              |  F  +------+  G  +--------+
                              +--+--+      +-----+        |
                                 |                        |
                                 |                        |
       +-----+    +-----+     +--+--+      +-----+     +--+--+
       |  A  +----+  B  +-----+  C  +--X---+  D  +-----+  E  |
       +-----+    +-----+     +-----+      +-----+     +-----+

         Figure 3: Resource Sharing in 1+R Recovery Scheme

   Using the network shown in Figure 3 as an example using 1+R recovery
   scheme, LSP1 (A-B-C-D-E) is the working LSP; assume it allows for
   resource sharing when the LSP traffic is dynamically restored.  Upon
   detecting the failure of a link along the LSP1, e.g., Link C-D, node
   A needs to decide which alternative path it will use to signal
   restoration LSP and reroute traffic.  In this case, A-B-C-F-G-E is
   chosen as the restoration LSP path, and the resources on the path
   segment A-B-C are reused by this LSP.  The working LSP is not torn
   down and coexists with the restoration LSP.  When the head-end node A
   signals the restoration LSP, nodes C, F, G, and E reconfigure the
   resources (as listed in Table 1 of this document) to set up the LSP
   by sending cross-connection command to the data plane.

   In the recovery scheme employing revertive behavior, after the
   failure is repaired, the resources on nodes C and E need to be
   reconfigured to set up the working LSP (using a procedure described
   in Section 4.3 of this document) by sending cross-connection command
   to the data plane.  The traffic is then reverted back to the original
   working LSP.

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4.  RSVP-TE Signaling Procedure

4.1.  Restoration LSP Association

   Where GMPLS end-to-end recovery scheme needs to employ a restoration
   LSP while keeping resources for the working and/or protecting LSPs
   reserved in the network after the failure, the restoration LSP is set
   up with an ASSOCIATION object that has the Association Type set to
   "Recovery" [RFC4872], the Association ID and the Association Source
   set to the corresponding Association ID and the Association Source
   signaled in the Path message of the LSP it is restoring.  For
   example, when a restoration LSP is signaled for a failed working LSP,
   the ASSOCIATION object in the Path message of the restoration LSP
   contains the Association ID and Association Source set to the
   Association ID and Association Source signaled in the working LSP for
   the "Recovery" Association Type.  Similarly, when a restoration LSP
   is set up for a failed protecting LSP, the ASSOCIATION object in the
   Path message of the restoration LSP contains the Association ID and
   Association Source is set to the Association ID and Association
   Source signaled in the protecting LSP for the "Recovery" Association
   Type.

   The procedure for signaling the PROTECTION object is specified in
   [RFC4872].  Specifically, the restoration LSP used for a working LSP
   is set up with the P bit cleared in the PROTECTION object in the Path
   message of the restoration LSP and the restoration LSP used for a
   protecting LSP is set up with the P bit set in the PROTECTION object
   in the Path message of the restoration LSP.

4.2.  Resource Sharing-Based Restoration LSP Setup

   GMPLS LSPs can share resources during LSP setup if they have the
   Shared Explicit (SE) flag set in the SESSION_ATTRIBUTE objects
   [RFC3209] in the Path messages that create them and:

   o  As defined in [RFC3209], LSPs have identical SESSION objects,
      and/or

   o  As defined in [RFC6689], LSPs have matching ASSOCIATION objects
      with the Association Type set to "Resource Sharing" signaled in
      their Path messages.  In this case, LSPs can have different
      SESSION objects i.e., a different Tunnel ID, Source and/or
      Destination signaled in their Path messages.

   As described in Section 2.5 of [RFC3209], the purpose of make-before-
   break is not to disrupt traffic, or adversely impact network
   operations while TE tunnel rerouting is in progress.  In non-packet
   transport networks, during the RSVP-TE signaling procedure, the nodes

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   set up cross-connections along the LSP accordingly.  Because the
   cross-connection cannot simultaneously connect a shared resource to
   different resources in two alternative LSPs, nodes may not be able to
   fulfill this request when LSPs share resources.

   For LSP restoration upon failure, as explained in Section 11 of
   [RFC4872], the reroute procedure may reuse existing resources.  The
   action of the intermediate nodes during the rerouting process to
   reconfigure cross-connections does not further impact the traffic
   since it has been interrupted due to the already failed LSP.

   The node actions for setting up the restoration LSP can be
   categorized into the following:

   -----------------------------------+---------------------------------
   |        Category                  |        Action                  |
   -----------------------------------+---------------------------------
   | Reusing existing resource on     | This type of node needs to     |
   | both input and output interfaces | reserve the existing resources |
   | (nodes A & B in Figure 3).       | and no cross-connection        |
   |                                  | command is needed.             |
   -----------------------------------+---------------------------------
   | Reusing an existing resource only| This type of node needs to     |
   | on one of the interfaces, either | reserve the resources and send |
   | input or output interfaces, and  | the reconfiguration            |
   | using new resource on the        | cross-connection command to its|
   | other interfaces.                | corresponding data plane       |
   | (nodes C & E in Figure 3).       | node on the interfaces where   |
   |                                  | new resources are needed, and  |
   |                                  | it needs to reuse the existing |
   |                                  | resources on the other         |
   |                                  | interfaces.                    |
   -----------------------------------+---------------------------------
   | Using new resources on both      | This type of node needs to     |
   | interfaces.                      | reserve the new resources      |
   | (nodes F & G in Figure 3).       | and send the cross-connection  |
   |                                  | command on both interfaces.    |
   -----------------------------------+---------------------------------

         Table 1: Node Actions during Restoration LSP Setup

   Depending on whether or not the resource is reused, the node actions
   differ.  This deviates from normal LSP setup, since some nodes do not
   need to reconfigure the cross-connection.  Also, the judgment of
   whether the control plane node needs to send a cross-connection setup
   or modification command to its corresponding data plane node(s)
   relies on the check whether the LSPs are sharing resources.

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4.3.  LSP Reversion

   If the end-to-end LSP recovery scheme employs the revertive behavior,
   as described in Section 3 of this document, traffic can be reverted
   from the restoration LSP to the working or protecting LSP after its
   failure is recovered.  The LSP reversion can be achieved using two
   methods:

   1. Make-While-Break Reversion: resources associated with a working or
      protecting LSP are reconfigured while removing reservations for
      the restoration LSP.

   2. Make-Before-Break Reversion: resources associated with a working
      or protecting LSP are reconfigured before removing reservations
      for the restoration LSP.

   In non-packet transport networks, both of the above reversion methods
   will result in some traffic disruption when the restoration LSP and
   the LSP being restored are sharing resources and the cross-
   connections need to be reconfigured on intermediate nodes.

4.3.1.  Make-While-Break Reversion

   In this reversion method, restoration LSP is simply requested to be
   deleted by the head-end.  Removing reservations for restoration LSP
   triggers reconfiguration of resources associated with a working or
   protecting LSP on every node where resources are shared.  The working
   or protecting LSP state was not removed from the nodes when the
   failure occurred.  Whenever reservation for restoration LSP is
   removed from a node, data plane configuration changes to reflect
   reservations of working or protecting LSP as signaling progresses.
   Eventually, after the whole restoration LSP is deleted, data plane
   configuration will fully match working or protecting LSP reservations
   on the whole path.  Thus, reversion is complete.

   Make-while-break, while being relatively simple in its logic, has a
   few limitations as follows which may not be acceptable in some
   networks:

   o  No rollback

   If, for some reason, reconfiguration of the data plane on one of the
   nodes, to match working or protecting LSP reservations, fails,
   falling back to restoration LSP is no longer an option, as its state
   might have already been removed from other nodes.

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   o  No completion guarantee

   Deletion of an LSP provides no guarantees of completion.  In
   particular, if RSVP packets are lost due to a node or link failure,
   it is possible for an LSP to be only partially deleted.  To mitigate
   this, RSVP could maintain soft state reservations and, hence,
   eventually remove remaining reservations due to refresh timeouts.
   This approach is not feasible in non-packet transport networks,
   however, where control and data channels are often separated; hence,
   soft state reservations are not useful.

   Finally, one could argue that graceful LSP deletion [RFC3473] would
   provide a guarantee of completion.  While this is true for most
   cases, many implementations will time out graceful deletion if LSP is
   not removed within certain amount of time, e.g., due to a transit
   node fault.  After that, deletion procedures that provide no
   completion guarantees will be attempted.  Hence, in corner cases a
   completion guarantee cannot be provided.

   o  No explicit notification of completion to head-end node

   In some cases, it may be useful for a head-end node to know when the
   data plane has been reconfigured to match working or protecting LSP
   reservations.  This knowledge could be used for initiating operations
   like enabling alarm monitoring, power equalization, and others.
   Unfortunately, for the reasons mentioned above, make-while-break
   reversion lacks such explicit notification.

4.3.2.  Make-Before-Break Reversion

   This reversion method can be used to overcome limitations of make-
   while-break reversion.  It is similar in spirit to the MBB concept
   used for re-optimization.  Instead of relying on deletion of the
   restoration LSP, the head-end chooses to establish a new reversion
   LSP that duplicates the configuration of the resources on the working
   or protecting LSP and uses identical ASSOCIATION and PROTECTION
   objects in the Path message of that LSP.  Only if the setup of this
   LSP is successful will other (restoration and working or protecting)
   LSPs be deleted by the head-end.  MBB reversion consists of two
   parts:

   A) Make part:

   Creating a new reversion LSP following working or protecting the LSP.
   The reversion LSP shares all of the resources of the working or
   protecting LSP and may share resources with the restoration LSP.  As
   the reversion LSP is created, resources are

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   reconfigured to match its reservations.  Hence, after the reversion
   LSP is created, data plane configuration reflects working or
   protecting LSP reservations.

   B) Break part:

   After the "make" part is finished, the original working or protecting
   and restoration LSPs are torn down, and the reversion LSP becomes the
   new working or protecting LSP.  Removing reservations for working or
   restoration LSPs does not cause any resource reconfiguration on the
   reversion LSP -- nodes follow same procedures for the "break" part of
   any MBB operation.  Hence, after working or protecting and
   restoration LSPs are removed, the data plane configuration is exactly
   the same as before starting restoration.  Thus, reversion is
   complete.

   MBB reversion uses make-before-break characteristics to overcome
   challenges related to make-while-break reversion as follow:

   o  Rollback

   If the "make" part fails, the (existing) restoration LSP will still
   be used to carry existing traffic as the restoration LSP state was
   not removed.  Same logic applies here as for any MBB operation
   failure.

   o  Completion guarantee

   LSP setup is resilient against RSVP message loss, as Path and Resv
   messages are refreshed periodically.  Hence, given that the network
   recovers from node and link failures eventually, reversion LSP setup
   is guaranteed to finish with either success or failure.

   o  Explicit notification of completion to head-end node

   The head-end knows that the data plane has been reconfigured to match
   working or protecting LSP reservations on the intermediate nodes when
   it receives a Resv message for the reversion LSP.

5.  Security Considerations

   This document reviews procedures defined in [RFC3209], [RFC4872],
   [RFC4873], and [RFC6689] and does not define any new procedures.
   This document does not introduce any new security issues; security
   issues were already covered in [RFC3209], [RFC4872], [RFC4873], and
   [RFC6689].

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6.  IANA Considerations

   This document does not require any IANA actions.

7.  References

7.1.  Normative References

   [RFC3209]   Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
               and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
               Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
               <http://www.rfc-editor.org/info/rfc3209>.

   [RFC3473]   Berger, L., Ed., "Generalized Multi-Protocol Label
               Switching (GMPLS) Signaling Resource ReserVation
               Protocol-Traffic Engineering (RSVP-TE) Extensions",
               RFC 3473, DOI 10.17487/RFC3473, January 2003,
               <http://www.rfc-editor.org/info/rfc3473>.

   [RFC4872]   Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
               Ed., "RSVP-TE Extensions in Support of End-to-End
               Generalized Multi-Protocol Label Switching (GMPLS)
               Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
               <http://www.rfc-editor.org/info/rfc4872>.

   [RFC4873]   Berger, L., Bryskin, I., Papadimitriou, D., and A.
               Farrel, "GMPLS Segment Recovery", RFC 4873,
               DOI 10.17487/RFC4873, May 2007,
               <http://www.rfc-editor.org/info/rfc4873>.

   [RFC6689]   Berger, L., "Usage of the RSVP ASSOCIATION Object",
               RFC 6689, DOI 10.17487/RFC6689, July 2012,
               <http://www.rfc-editor.org/info/rfc6689>.

7.2.  Informative References

   [RFC3945]   Mannie, E., Ed., "Generalized Multi-Protocol Label
               Switching (GMPLS) Architecture", RFC 3945,
               DOI 10.17487/RFC3945, October 2004,
               <http://www.rfc-editor.org/info/rfc3945>.

   [RFC4203]   Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
               in Support of Generalized Multi-Protocol Label Switching
               (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
               <http://www.rfc-editor.org/info/rfc4203>.

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   [RFC4426]   Lang, J., Ed., Rajagopalan, B., Ed., and D.
               Papadimitriou, Ed., "Generalized Multi-Protocol Label
               Switching (GMPLS) Recovery Functional Specification",
               RFC 4426, DOI 10.17487/RFC4426, March 2006,
               <http://www.rfc-editor.org/info/rfc4426>.

   [RFC4427]   Mannie, E., Ed., and D. Papadimitriou, Ed., "Recovery
               (Protection and Restoration) Terminology for Generalized
               Multi-Protocol Label Switching (GMPLS)", RFC 4427,
               DOI 10.17487/RFC4427, March 2006,
               <http://www.rfc-editor.org/info/rfc4427>.

Acknowledgements

   The authors would like to thank:

   -  George Swallow for the discussions on the GMPLS restoration.

   -  Lou Berger for the guidance on this work.

   -  Lou Berger, Vishnu Pavan Beeram, and Christian Hopps for reviewing
      this document and providing valuable comments.

   A special thanks to Dale Worley for his thorough review of this
   document.

Contributors

   Gabriele Maria Galimberti
   Cisco Systems, Inc.

   Email: ggalimbe@cisco.com

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Authors' Addresses

   Xian Zhang
   Huawei Technologies
   F3-1-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129
   China

   Email: zhang.xian@huawei.com


   Haomian Zheng (editor)
   Huawei Technologies
   F3-1-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129
   China

   Email: zhenghaomian@huawei.com


   Rakesh Gandhi (editor)
   Cisco Systems, Inc.

   Email: rgandhi@cisco.com


   Zafar Ali
   Cisco Systems, Inc.

   Email: zali@cisco.com


   Pawel Brzozowski
   ADVA Optical

   Email: PBrzozowski@advaoptical.com